In recent years, various full color copiers and printers of the electrophotographic type have been proposed. Developing apparatus used in such copiers and printers typically require four developing units, which respectively accommodate colored toner of cyan (C), magenta (M), yellow (Y), and black (Bk), the first three of which correspond to the three primary colors of red (R), green (G), and blue (B). Each of the four developing units is capable of being switched to an operative position commonly referred to as the "developing position."
A common full color developing apparatus is a rotary type wherein a plurality of developing units are integratedly supported by a support member capable of being rotated at a predetermined angle employing a motor as a drive source. "High-speed" switching of the developing units (e.g., switching in about 0.4 second or less) is determined from the perspective of high-speed image formation. When carrying out high-speed switching using a motor as a drive source, however, a powerful and expensive motor must be used. This is disadvantageous because it adds to the cost of manufacture of the apparatus and typically requires more energy to power the motor.
In such full color developing apparatus of the conventional rotary type, the individual developing units are typically fixedly mounted on the support member. When the developing units are exchanged or replaced, however, the positioning of the developing units must be precisely adjusted relative to the photoconductive member, which requires the inclusion of a high-precision mechanism in the rotary apparatus and complex fine-adjustment by skilled personnel. This also increases over-all costs.